perf tools: Don't assume that the parser returns non empty evsel list

Don't blindly retrieve and use a last element in the lists returned by
parse_events__scanner(), as it may have collected no entries, i.e.
return an empty list.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1441523623-152703-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 0fde5293a38e8aa42bd955faecf48e4975971594..61c2bc20926d215978e0b7133964a99d920fa0e0 100644 (file)
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -827,6 +827,11 @@ void parse_events__set_leader(char *name, struct list_head *list)
 {
        struct perf_evsel *leader;
 
+       if (list_empty(list)) {
+               WARN_ONCE(true, "WARNING: failed to set leader: empty list");
+               return;
+       }
+
        __perf_evlist__set_leader(list);
        leader = list_entry(list->next, struct perf_evsel, node);
        leader->group_name = name ? strdup(name) : NULL;
@@ -1176,6 +1181,11 @@ int parse_events(struct perf_evlist *evlist, const char *str,
        if (!ret) {
                struct perf_evsel *last;
 
+               if (list_empty(&data.list)) {
+                       WARN_ONCE(true, "WARNING: event parser found nothing");
+                       return -1;
+               }
+
                perf_evlist__splice_list_tail(evlist, &data.list);
                evlist->nr_groups += data.nr_groups;
                last = perf_evlist__last(evlist);
@@ -1285,6 +1295,12 @@ foreach_evsel_in_last_glob(struct perf_evlist *evlist,
        struct perf_evsel *last = NULL;
        int err;
 
+       /*
+        * Don't return when list_empty, give func a chance to report
+        * error when it found last == NULL.
+        *
+        * So no need to WARN here, let *func do this.
+        */
        if (evlist->nr_entries > 0)
                last = perf_evlist__last(evlist);